1. Field of the Invention
This invention relates to a dispensing system, in particular one which may be of use for example in the dispensing of small quantities of medicament, where the medicament is required to be dispensed in aerosol from.
2. Brief Description of Art
It is known for dosing systems which supply a nebulized substance to containing a metering system. For example, in GB 1,568,808 (Rosenthal) there is described a metering system for supplying a nebulized substance for patient inhalation comprising a nebulizing means, a detecting means for detecting the initiation of the patient's inhalation, an adjustable timing means for adjusting a timed operation, and a valve means which is controlled by the timing means, in order to provide a controlled dosage of nebulized substance.
However, for this system to work and provide a precise dose of medicament, it is necessary that the system utilises a calibrated nebulizer which has a precise rate of output against time. Commercially available nebulizers have a wide range of outputs against time. In addition, the calibration must remain constant over the use of the nebulizer, and the nebulizer must be connected to the dosing device in such a way that the calibration of the nebulizer is valid and recognised when operated with the dispensing device. This is particularly important in relation to the length of tube between the value and the nebulizer.
Also, it is noted that this application describes no teaching of a device which is in any way calibrated for use with nominated drugs. This may have been due to the fact that the apparatus embodied in this application is designed for provocation testing, which is generally carried out in a laboratory, and is used to deliver pulses of aerosol into a patient's airway in order to determine their reactivity to allergens. The apparatus is not designed as one for a patient to take home, and to deliver precise does of medicament on a day to day basis.
In addition to the above application, GB 2,164,569 (Etela-Hameen Kauhkovammayhdiatys RY (Finland)) describes a similar system to that described above, which is also designed for provocation testing, except that it has an additional atomizing starting time control, which is used for selecting the atomizing starting moment to coincide with the beginning of the inspiration phase, which is found by examination to be favourable for a particular patient.
EP 519,742 (DeVilbiss Healthcare Inc.) describes a medical nebulizer control system which has three way valve. In the embodiment, one part of the valve is connected to a pressure sensor, and another is connected to a compressed air supply. The control system within this apparatus uses the supply tube to the nebulizer to detect the patient's breathing pattern. When it detects inhalation, it switches the valve over to the compressed air supply, which them drives the nebulizer for a predetermined period of time irrespective of whether the patient has continued to inhale or not. This device also suffers from the problems of other nebulizers in that there is a long length of tube between the control box and the nebulizer. In addition the nebulizer can be supplied from any manufacturer, and hence its calibration is not tied into the device, thereby causing variable amounts of medicament to be dispensed.